Recently, electronic parts such as resistances, condensers and integrated circuits have been miniaturized and used in the form of chips. To accomodate such a tendency, various devices for packaging such chips suitable for use in storage, transportation and automatic retrieval of the packaged chips have been proposed. Among others, devices based on a carrier tape appear to have the most promising prospects.
Such devices may be roughly classified into two types: (a) one using a carrier tape having apertures punched out, as disclosed in Japanese Utility Model Laid-open Publication No. 58-7,399, and (b) the other using an embossed carrier tape, as disclosed in Japanese Utility Model Laid-open Publication Nos. 62-65,959 and 61-202,362.
In the first type of device, use is made, as a carrier tape, of a relatively thick tape of paper having a row of apertures of a required dimension formed along the center line of the tape with a predetermined interval between successive apertures. Normally, another row of holes are provided along one of side edges of the carrier tape for the purpose of feeding the tape. A bottom tape is attached to one surface of the carrier tape so that each aperture forms a chip-holding space. After chips have been placed in respective chip-holding spaces, a cover tape is attached to the other surface of the carrier tape so as to seal the chips in position.
In the second type of device, as shown in FIG. 4, use is made, as a carrier tape, of an embossed plastic tape 3 having a row of depressed parts (chip-holding parts 1) of a required dimension formed along the center line of the tape with a predetermined interval between successive parts. Normally, another row of holes 2 are provided along one of side edges of the carrier tape for the purpose of feeding the tape. After chips 4 have been placed in respective chip-holding parts, a cover tape 5 is attached to the surface of the carrier tape so as to seal the chips 4 in position.
In both the types of devices, use is made of a cover tape 5, which normally comprises a base plastic tape 6 and a layer 7 of a heat sensitive adhesive formed on the base tape 6, which adhesive is inactive at ambient temperature and becomes active only when heated. Such a cover tape 5 is adhered to the carrier tape by application of heat and pressure particularly to those areas adjacent to the chip-holding parts 1.
The cover tape is required to firmly adhere to the carrier tape on the one hand. On the other hand, for retrieval of the stored chips, it is required that the cover tape can be peeled off from the carrier tape by a relatively weak force. Further, the chips must not be stained by the adhesive constituting the adhesive layer 7. In other words, the chips 4 should not come in contact with the adhesive layer 7 at least under conditions where the adhesive is active.
For these requirements, hot melt adhesives have heretofore been generally employed as the adhesive layer 7. However, problems have been associated with the hot melt adhesives in that the cover tape 5 must be adhered to the carrier tape 3 under heat in areas along both side edges having the cover tape 5 of a width of on the order of about one millimeter, frequently resulting in non-uniform adhesion. The step of adhesion under heat is also disadvantageous from the view point of the productive speed of the production line, and might invite undesirable heat deformation of the carrier tape 3. Further, in a case wherein the chips 4 are stored or transported at an elevated temperature, the hot melt adhesive is reactivated and might come in contact with the chips 4 to stain them.